diff --git a/src/fsfw/cfdp/FileSize.h b/src/fsfw/cfdp/Fss.h
similarity index 93%
rename from src/fsfw/cfdp/FileSize.h
rename to src/fsfw/cfdp/Fss.h
index b0b48452..fbfc1e9a 100644
--- a/src/fsfw/cfdp/FileSize.h
+++ b/src/fsfw/cfdp/Fss.h
@@ -8,11 +8,11 @@
 
 namespace cfdp {
 
-struct FileSize : public SerializeIF {
+struct Fss : public SerializeIF {
  public:
-  FileSize() = default;
+  Fss() = default;
 
-  explicit FileSize(uint64_t fileSize, bool isLarge = false) { setFileSize(fileSize, isLarge); };
+  explicit Fss(uint64_t fileSize, bool isLarge = false) { setFileSize(fileSize, isLarge); };
 
   [[nodiscard]] uint64_t value() const { return fileSize; }
 
diff --git a/src/fsfw/cfdp/handler/DestHandler.cpp b/src/fsfw/cfdp/handler/DestHandler.cpp
index 4018e7d6..f44f5d41 100644
--- a/src/fsfw/cfdp/handler/DestHandler.cpp
+++ b/src/fsfw/cfdp/handler/DestHandler.cpp
@@ -158,7 +158,7 @@ ReturnValue_t cfdp::DestHandler::handleFileDataPdu(const cfdp::PacketInfo& info)
     // TODO: This is not a CFDP error. Event and/or warning?
     return constAccessorPair.first;
   }
-  cfdp::FileSize offset;
+  cfdp::Fss offset;
   FileDataInfo fdInfo(offset);
   FileDataReader reader(constAccessorPair.second.data(), constAccessorPair.second.size(), fdInfo);
   ReturnValue_t result = reader.parseData();
diff --git a/src/fsfw/cfdp/handler/DestHandler.h b/src/fsfw/cfdp/handler/DestHandler.h
index 7777c08f..40fe5e10 100644
--- a/src/fsfw/cfdp/handler/DestHandler.h
+++ b/src/fsfw/cfdp/handler/DestHandler.h
@@ -131,7 +131,7 @@ class DestHandler {
     uint16_t vfsErrorCount = 0;
     std::vector<char> sourceName;
     std::vector<char> destName;
-    cfdp::FileSize fileSize;
+    cfdp::Fss fileSize;
     TransactionId transactionId;
     PduConfig pduConf;
     ConditionCode conditionCode = ConditionCode::NO_ERROR;
diff --git a/src/fsfw/cfdp/handler/SourceHandler.cpp b/src/fsfw/cfdp/handler/SourceHandler.cpp
index 074bd73f..45d9d4e6 100644
--- a/src/fsfw/cfdp/handler/SourceHandler.cpp
+++ b/src/fsfw/cfdp/handler/SourceHandler.cpp
@@ -125,6 +125,9 @@ ReturnValue_t cfdp::SourceHandler::putRequest(PutRequestFull& putRequest, Remote
   if (!sourceParams.user.vfs.fileExists(params)) {
     return FILE_DOES_NOT_EXIST;
   }
+  if (cfg.maxFileSegmentLen > fileBuf.size() or cfg.maxFileSegmentLen == 0) {
+    return FILE_SEGMENT_LEN_INVALID;
+  }
   transactionParams.closureRequested = putRequest.closureRequested;
   transactionParams.pduConf.mode = putRequest.transmissionMode;
   transactionParams.pduConf.destId = putRequest.destId;
@@ -138,52 +141,60 @@ ReturnValue_t cfdp::SourceHandler::putRequest(PutRequestFull& putRequest, Remote
     state = cfdp::CfdpState::BUSY_CLASS_1_NACKED;
   }
   step = TransactionStep::IDLE;
-  size_t fileSize = 0;
+  uint64_t fileSize = 0;
   sourceParams.user.vfs.getFileSize(params, fileSize);
   transactionParams.pduConf.largeFile = false;
   if (fileSize > UINT32_MAX) {
     transactionParams.pduConf.largeFile = true;
   }
   transactionParams.fileSize.setFileSize(fileSize, transactionParams.pduConf.largeFile);
-  currentRemoteCfg = cfg;
+  transactionParams.remoteCfg = cfg;
   return OK;
 }
 
 ReturnValue_t cfdp::SourceHandler::prepareAndSendMetadataPdu() {
   cfdp::StringLv sourceName(transactionParams.sourceName.data(), transactionParams.sourceNameSize);
-  cfdp::StringLv destName(transactionParams.sourceName.data(), transactionParams.sourceNameSize);
+  cfdp::StringLv destName(transactionParams.destName.data(), transactionParams.destNameSize);
   auto metadataInfo = MetadataInfo(transactionParams.fileSize, sourceName, destName);
   auto metadataPdu = MetadataPduCreator(transactionParams.pduConf, metadataInfo);
-  uint8_t* dataPtr;
-  store_address_t storeId;
-  ReturnValue_t result =
-      fsfwParams.tcStore->getFreeElement(&storeId, metadataPdu.getSerializedSize(), &dataPtr);
-  if (result != OK) {
-    // TODO: Better error handling?
-    return result;
-  }
-  size_t serializedLen = 0;
-  result = metadataPdu.serializeBe(dataPtr, serializedLen, metadataPdu.getSerializedSize());
-  if (result != OK) {
-    return result;
-  }
-  TmTcMessage tcMsg(storeId);
-  result =
-      fsfwParams.msgQueue->sendMessage(fsfwParams.packetDest.getReportReceptionQueue(), &tcMsg);
-  if (result != OK) {
-    return result;
-  }
+  sendGenericPdu(metadataPdu);
   // Advance FSM if everything works
   step = TransactionStep::SENDING_FILE_DATA;
   return OK;
 }
 
 ReturnValue_t cfdp::SourceHandler::prepareAndSendNextFileDataPdu() {
-  // TODO: Implement
-  // auto fileDataInfo = FileDataInfo(transactionParams.fileSize);
-  // auto fileDataPdu = FileDataCreator();
-  // Advance FSM after all file data PDUs were sent
-  step = TransactionStep::SENDING_EOF;
+  cfdp::Fss offset(transactionParams.progress);
+  uint64_t readLen;
+  uint64_t fileSize = transactionParams.fileSize.value();
+  if (fileSize == 0) {
+    // We are done, no need to send file data PDUs for an empty file.
+    step = TransactionStep::SENDING_EOF;
+    return OK;
+  }
+  if (fileSize < transactionParams.remoteCfg.maxFileSegmentLen) {
+    readLen = transactionParams.fileSize.value();
+  } else {
+    if (transactionParams.progress + transactionParams.remoteCfg.maxFileSegmentLen > fileSize) {
+      readLen = fileSize - transactionParams.progress;
+    } else {
+      readLen = transactionParams.remoteCfg.maxFileSegmentLen;
+    }
+  }
+  FileOpParams fileParams(transactionParams.sourceName.data(), readLen);
+  ReturnValue_t result =
+      sourceParams.user.vfs.readFromFile(fileParams, fileBuf.data(), fileBuf.size());
+  if (result != returnvalue::OK) {
+    return result;
+  }
+  auto fileDataInfo = FileDataInfo(offset, fileBuf.data(), readLen);
+  auto fileDataPdu = FileDataCreator(transactionParams.pduConf, fileDataInfo);
+  sendGenericPdu(fileDataPdu);
+  transactionParams.progress += readLen;
+  if (transactionParams.progress >= fileSize) {
+    // Advance FSM after all file data PDUs were sent.
+    step = TransactionStep::SENDING_EOF;
+  }
   return OK;
 }
 
@@ -213,3 +224,21 @@ ReturnValue_t cfdp::SourceHandler::initialize() {
   }
   return OK;
 }
+
+ReturnValue_t cfdp::SourceHandler::sendGenericPdu(const SerializeIF& pdu) const {
+  uint8_t* dataPtr;
+  store_address_t storeId;
+  ReturnValue_t result =
+      fsfwParams.tcStore->getFreeElement(&storeId, pdu.getSerializedSize(), &dataPtr);
+  if (result != OK) {
+    // TODO: Better error handling?
+    return result;
+  }
+  size_t serializedLen = 0;
+  result = pdu.serializeBe(dataPtr, serializedLen, pdu.getSerializedSize());
+  if (result != OK) {
+    return result;
+  }
+  TmTcMessage tcMsg(storeId);
+  return fsfwParams.msgQueue->sendMessage(fsfwParams.packetDest.getReportReceptionQueue(), &tcMsg);
+}
diff --git a/src/fsfw/cfdp/handler/SourceHandler.h b/src/fsfw/cfdp/handler/SourceHandler.h
index 98850472..059c9864 100644
--- a/src/fsfw/cfdp/handler/SourceHandler.h
+++ b/src/fsfw/cfdp/handler/SourceHandler.h
@@ -6,7 +6,7 @@
 
 #include "UserBase.h"
 #include "defs.h"
-#include "fsfw/cfdp/FileSize.h"
+#include "fsfw/cfdp/Fss.h"
 #include "fsfw/cfdp/handler/mib.h"
 #include "fsfw/events/EventReportingProxyIF.h"
 #include "fsfw/storagemanager/StorageManagerIF.h"
@@ -64,16 +64,17 @@ class SourceHandler {
     size_t sourceNameSize = 0;
     std::array<char, 524> destName{};
     size_t destNameSize = 0;
-    cfdp::FileSize fileSize;
-    size_t currentFilePos = 0;
+    cfdp::Fss fileSize;
+    size_t progress = 0;
     bool closureRequested = false;
+    RemoteEntityCfg remoteCfg;
     PduConfig pduConf;
   } transactionParams;
   cfdp::CfdpState state = cfdp::CfdpState::IDLE;
   TransactionStep step = TransactionStep::IDLE;
+  std::array<uint8_t, 4096> fileBuf{};
   SourceHandlerParams sourceParams;
   cfdp::FsfwParams fsfwParams;
-  RemoteEntityCfg currentRemoteCfg;
   FsmResult fsmResult;
 
   FsmResult& fsmNacked();
@@ -81,6 +82,8 @@ class SourceHandler {
   ReturnValue_t prepareAndSendMetadataPdu();
   ReturnValue_t prepareAndSendNextFileDataPdu();
   ReturnValue_t prepareAndSendEofPdu();
+
+  ReturnValue_t sendGenericPdu(const SerializeIF& pdu) const;
 };
 
 }  // namespace cfdp
diff --git a/src/fsfw/cfdp/handler/defs.h b/src/fsfw/cfdp/handler/defs.h
index dc300e7e..81a8895c 100644
--- a/src/fsfw/cfdp/handler/defs.h
+++ b/src/fsfw/cfdp/handler/defs.h
@@ -74,6 +74,7 @@ static constexpr Event FILENAME_TOO_LARGE_ERROR = event::makeEvent(SSID, 4, seve
 
 static constexpr ReturnValue_t SOURCE_TRANSACTION_PENDING = returnvalue::makeCode(CID, 0);
 static constexpr ReturnValue_t FILE_DOES_NOT_EXIST = returnvalue::makeCode(CID, 1);
+static constexpr ReturnValue_t FILE_SEGMENT_LEN_INVALID = returnvalue::makeCode(CID, 1);
 
 }  // namespace cfdp
 #endif  // FSFW_CFDP_HANDLER_DEFS_H
diff --git a/src/fsfw/cfdp/pdu/EofInfo.cpp b/src/fsfw/cfdp/pdu/EofInfo.cpp
index 98e79df7..e3df5c88 100644
--- a/src/fsfw/cfdp/pdu/EofInfo.cpp
+++ b/src/fsfw/cfdp/pdu/EofInfo.cpp
@@ -1,6 +1,6 @@
 #include "EofInfo.h"
 
-EofInfo::EofInfo(cfdp::ConditionCode conditionCode, uint32_t checksum, cfdp::FileSize fileSize,
+EofInfo::EofInfo(cfdp::ConditionCode conditionCode, uint32_t checksum, cfdp::Fss fileSize,
                  EntityIdTlv* faultLoc)
     : conditionCode(conditionCode), checksum(checksum), fileSize(fileSize), faultLoc(faultLoc) {}
 
@@ -16,7 +16,7 @@ cfdp::ConditionCode EofInfo::getConditionCode() const { return conditionCode; }
 
 EntityIdTlv* EofInfo::getFaultLoc() const { return faultLoc; }
 
-cfdp::FileSize& EofInfo::getFileSize() { return fileSize; }
+cfdp::Fss& EofInfo::getFileSize() { return fileSize; }
 
 void EofInfo::setChecksum(uint32_t checksum) { this->checksum = checksum; }
 
diff --git a/src/fsfw/cfdp/pdu/EofInfo.h b/src/fsfw/cfdp/pdu/EofInfo.h
index 4b4fb057..59bfed31 100644
--- a/src/fsfw/cfdp/pdu/EofInfo.h
+++ b/src/fsfw/cfdp/pdu/EofInfo.h
@@ -1,14 +1,14 @@
 #ifndef FSFW_SRC_FSFW_CFDP_PDU_EOFINFO_H_
 #define FSFW_SRC_FSFW_CFDP_PDU_EOFINFO_H_
 
-#include "../FileSize.h"
+#include "../Fss.h"
 #include "../definitions.h"
 #include "fsfw/cfdp/tlv/EntityIdTlv.h"
 
 struct EofInfo {
  public:
   explicit EofInfo(EntityIdTlv* faultLoc = nullptr);
-  EofInfo(cfdp::ConditionCode conditionCode, uint32_t checksum, cfdp::FileSize fileSize,
+  EofInfo(cfdp::ConditionCode conditionCode, uint32_t checksum, cfdp::Fss fileSize,
           EntityIdTlv* faultLoc = nullptr);
 
   size_t getSerializedSize(bool fssLarge = false);
@@ -17,7 +17,7 @@ struct EofInfo {
   [[nodiscard]] cfdp::ConditionCode getConditionCode() const;
 
   [[nodiscard]] EntityIdTlv* getFaultLoc() const;
-  cfdp::FileSize& getFileSize();
+  cfdp::Fss& getFileSize();
   void setChecksum(uint32_t checksum);
   void setConditionCode(cfdp::ConditionCode conditionCode);
   void setFaultLoc(EntityIdTlv* faultLoc);
@@ -26,7 +26,7 @@ struct EofInfo {
  private:
   cfdp::ConditionCode conditionCode;
   uint32_t checksum;
-  cfdp::FileSize fileSize;
+  cfdp::Fss fileSize;
   EntityIdTlv* faultLoc = nullptr;
 };
 
diff --git a/src/fsfw/cfdp/pdu/FileDataCreator.cpp b/src/fsfw/cfdp/pdu/FileDataCreator.cpp
index 956752fb..70779a51 100644
--- a/src/fsfw/cfdp/pdu/FileDataCreator.cpp
+++ b/src/fsfw/cfdp/pdu/FileDataCreator.cpp
@@ -37,7 +37,7 @@ ReturnValue_t FileDataCreator::serialize(uint8_t** buffer, size_t* size, size_t
     *buffer += segmentMetadataLen;
     *size += segmentMetadataLen;
   }
-  cfdp::FileSize& offset = info.getOffset();
+  cfdp::Fss& offset = info.getOffset();
   result = offset.serialize(this->getLargeFileFlag(), buffer, size, maxSize, streamEndianness);
   if (result != returnvalue::OK) {
     return result;
diff --git a/src/fsfw/cfdp/pdu/FileDataInfo.cpp b/src/fsfw/cfdp/pdu/FileDataInfo.cpp
index 19fc00cd..ec12e9da 100644
--- a/src/fsfw/cfdp/pdu/FileDataInfo.cpp
+++ b/src/fsfw/cfdp/pdu/FileDataInfo.cpp
@@ -1,9 +1,9 @@
 #include "FileDataInfo.h"
 
-FileDataInfo::FileDataInfo(cfdp::FileSize &offset, const uint8_t *fileData, size_t fileSize)
+FileDataInfo::FileDataInfo(cfdp::Fss &offset, const uint8_t *fileData, size_t fileSize)
     : offset(offset), fileData(fileData), fileSize(fileSize) {}
 
-FileDataInfo::FileDataInfo(cfdp::FileSize &offset) : offset(offset) {}
+FileDataInfo::FileDataInfo(cfdp::Fss &offset) : offset(offset) {}
 
 void FileDataInfo::setSegmentMetadataFlag(bool enable) {
   if (enable) {
@@ -71,7 +71,7 @@ const uint8_t *FileDataInfo::getSegmentMetadata(size_t *segmentMetadataLen_) {
   return segmentMetadata;
 }
 
-cfdp::FileSize &FileDataInfo::getOffset() { return offset; }
+cfdp::Fss &FileDataInfo::getOffset() { return offset; }
 
 void FileDataInfo::setRecordContinuationState(cfdp::RecordContinuationState recContState) {
   this->recContState = recContState;
diff --git a/src/fsfw/cfdp/pdu/FileDataInfo.h b/src/fsfw/cfdp/pdu/FileDataInfo.h
index 36908d8b..2721cda2 100644
--- a/src/fsfw/cfdp/pdu/FileDataInfo.h
+++ b/src/fsfw/cfdp/pdu/FileDataInfo.h
@@ -1,17 +1,17 @@
 #ifndef FSFW_SRC_FSFW_CFDP_PDU_FILEDATAINFO_H_
 #define FSFW_SRC_FSFW_CFDP_PDU_FILEDATAINFO_H_
 
-#include <fsfw/cfdp/FileSize.h>
+#include <fsfw/cfdp/Fss.h>
 #include <fsfw/cfdp/definitions.h>
 
 class FileDataInfo {
  public:
-  explicit FileDataInfo(cfdp::FileSize& offset);
-  FileDataInfo(cfdp::FileSize& offset, const uint8_t* fileData, size_t fileSize);
+  explicit FileDataInfo(cfdp::Fss& offset);
+  FileDataInfo(cfdp::Fss& offset, const uint8_t* fileData, size_t fileSize);
 
   [[nodiscard]] size_t getSerializedSize(bool largeFile = false) const;
 
-  cfdp::FileSize& getOffset();
+  cfdp::Fss& getOffset();
   const uint8_t* getFileData(size_t* fileSize = nullptr) const;
   void setFileData(const uint8_t* fileData, size_t fileSize);
 
@@ -33,7 +33,7 @@ class FileDataInfo {
  private:
   cfdp::SegmentMetadataFlag segmentMetadataFlag = cfdp::SegmentMetadataFlag::NOT_PRESENT;
   cfdp::SegmentationControl segCtrl = cfdp::SegmentationControl::NO_RECORD_BOUNDARIES_PRESERVATION;
-  cfdp::FileSize& offset;
+  cfdp::Fss& offset;
   const uint8_t* fileData = nullptr;
   size_t fileSize = 0;
   cfdp::RecordContinuationState recContState = cfdp::RecordContinuationState::NO_START_NO_END;
diff --git a/src/fsfw/cfdp/pdu/KeepAlivePduCreator.cpp b/src/fsfw/cfdp/pdu/KeepAlivePduCreator.cpp
index 40747751..2afcd427 100644
--- a/src/fsfw/cfdp/pdu/KeepAlivePduCreator.cpp
+++ b/src/fsfw/cfdp/pdu/KeepAlivePduCreator.cpp
@@ -1,6 +1,6 @@
 #include "KeepAlivePduCreator.h"
 
-KeepAlivePduCreator::KeepAlivePduCreator(PduConfig &conf, cfdp::FileSize &progress)
+KeepAlivePduCreator::KeepAlivePduCreator(PduConfig &conf, cfdp::Fss &progress)
     : FileDirectiveCreator(conf, cfdp::FileDirective::KEEP_ALIVE, 4), progress(progress) {
   updateDirectiveFieldLen();
 }
diff --git a/src/fsfw/cfdp/pdu/KeepAlivePduCreator.h b/src/fsfw/cfdp/pdu/KeepAlivePduCreator.h
index aa4bf0fd..97ce6095 100644
--- a/src/fsfw/cfdp/pdu/KeepAlivePduCreator.h
+++ b/src/fsfw/cfdp/pdu/KeepAlivePduCreator.h
@@ -1,12 +1,12 @@
 #ifndef FSFW_CFDP_PDU_KEEPALIVEPDUSERIALIZER_H_
 #define FSFW_CFDP_PDU_KEEPALIVEPDUSERIALIZER_H_
 
-#include "fsfw/cfdp/FileSize.h"
+#include "fsfw/cfdp/Fss.h"
 #include "fsfw/cfdp/pdu/FileDirectiveCreator.h"
 
 class KeepAlivePduCreator : public FileDirectiveCreator {
  public:
-  KeepAlivePduCreator(PduConfig& conf, cfdp::FileSize& progress);
+  KeepAlivePduCreator(PduConfig& conf, cfdp::Fss& progress);
 
   void updateDirectiveFieldLen();
 
@@ -16,7 +16,7 @@ class KeepAlivePduCreator : public FileDirectiveCreator {
                           Endianness streamEndianness) const override;
 
  private:
-  cfdp::FileSize& progress;
+  cfdp::Fss& progress;
 };
 
 #endif /* FSFW_CFDP_PDU_KEEPALIVEPDUSERIALIZER_H_ */
diff --git a/src/fsfw/cfdp/pdu/KeepAlivePduReader.cpp b/src/fsfw/cfdp/pdu/KeepAlivePduReader.cpp
index d3362cf9..73ddc678 100644
--- a/src/fsfw/cfdp/pdu/KeepAlivePduReader.cpp
+++ b/src/fsfw/cfdp/pdu/KeepAlivePduReader.cpp
@@ -1,7 +1,6 @@
 #include "KeepAlivePduReader.h"
 
-KeepAlivePduReader::KeepAlivePduReader(const uint8_t* pduBuf, size_t maxSize,
-                                       cfdp::FileSize& progress)
+KeepAlivePduReader::KeepAlivePduReader(const uint8_t* pduBuf, size_t maxSize, cfdp::Fss& progress)
     : FileDirectiveReader(pduBuf, maxSize), progress(progress) {}
 
 ReturnValue_t KeepAlivePduReader::parseData() {
@@ -15,4 +14,4 @@ ReturnValue_t KeepAlivePduReader::parseData() {
   return progress.deSerialize(&buffer, &remLen, getEndianness());
 }
 
-cfdp::FileSize& KeepAlivePduReader::getProgress() { return progress; }
+cfdp::Fss& KeepAlivePduReader::getProgress() { return progress; }
diff --git a/src/fsfw/cfdp/pdu/KeepAlivePduReader.h b/src/fsfw/cfdp/pdu/KeepAlivePduReader.h
index 38e061f1..553101c9 100644
--- a/src/fsfw/cfdp/pdu/KeepAlivePduReader.h
+++ b/src/fsfw/cfdp/pdu/KeepAlivePduReader.h
@@ -1,19 +1,19 @@
 #ifndef FSFW_CFDP_PDU_KEEPALIVEREADER_H_
 #define FSFW_CFDP_PDU_KEEPALIVEREADER_H_
 
-#include "fsfw/cfdp/FileSize.h"
+#include "fsfw/cfdp/Fss.h"
 #include "fsfw/cfdp/pdu/FileDirectiveReader.h"
 
 class KeepAlivePduReader : public FileDirectiveReader {
  public:
-  KeepAlivePduReader(const uint8_t* pduBuf, size_t maxSize, cfdp::FileSize& progress);
+  KeepAlivePduReader(const uint8_t* pduBuf, size_t maxSize, cfdp::Fss& progress);
 
   ReturnValue_t parseData() override;
 
-  cfdp::FileSize& getProgress();
+  cfdp::Fss& getProgress();
 
  private:
-  cfdp::FileSize& progress;
+  cfdp::Fss& progress;
 };
 
 #endif /* FSFW_CFDP_PDU_KEEPALIVEPDUREADER_H_ */
diff --git a/src/fsfw/cfdp/pdu/MetadataInfo.cpp b/src/fsfw/cfdp/pdu/MetadataInfo.cpp
index d88bdd87..180549e5 100644
--- a/src/fsfw/cfdp/pdu/MetadataInfo.cpp
+++ b/src/fsfw/cfdp/pdu/MetadataInfo.cpp
@@ -1,14 +1,14 @@
 #include "MetadataInfo.h"
 
 MetadataInfo::MetadataInfo(bool closureRequested, cfdp::ChecksumType checksumType,
-                           cfdp::FileSize& fileSize, cfdp::StringLv& sourceFileName,
+                           cfdp::Fss& fileSize, cfdp::StringLv& sourceFileName,
                            cfdp::StringLv& destFileName)
     : MetadataInfo(fileSize, sourceFileName, destFileName) {
   this->closureRequested = closureRequested;
   this->checksumType = checksumType;
 }
 
-MetadataInfo::MetadataInfo(cfdp::FileSize& fileSize, cfdp::StringLv& sourceFileName,
+MetadataInfo::MetadataInfo(cfdp::Fss& fileSize, cfdp::StringLv& sourceFileName,
                            cfdp::StringLv& destFileName)
     : fileSize(fileSize), sourceFileName(sourceFileName), destFileName(destFileName) {}
 
@@ -37,7 +37,7 @@ void MetadataInfo::setClosureRequested(bool closureRequested_) {
 
 cfdp::StringLv& MetadataInfo::getDestFileName() { return destFileName; }
 
-cfdp::FileSize& MetadataInfo::getFileSize() { return fileSize; }
+cfdp::Fss& MetadataInfo::getFileSize() { return fileSize; }
 
 ReturnValue_t MetadataInfo::getOptions(cfdp::Tlv*** optionsArray_, size_t* optionsLen_,
                                        size_t* maxOptsLen) {
diff --git a/src/fsfw/cfdp/pdu/MetadataInfo.h b/src/fsfw/cfdp/pdu/MetadataInfo.h
index 95f4544a..7ae269a9 100644
--- a/src/fsfw/cfdp/pdu/MetadataInfo.h
+++ b/src/fsfw/cfdp/pdu/MetadataInfo.h
@@ -3,7 +3,7 @@
 
 #include <optional>
 
-#include "fsfw/cfdp/FileSize.h"
+#include "fsfw/cfdp/Fss.h"
 #include "fsfw/cfdp/definitions.h"
 #include "fsfw/cfdp/tlv/Lv.h"
 #include "fsfw/cfdp/tlv/StringLv.h"
@@ -11,9 +11,8 @@
 
 class MetadataInfo {
  public:
-  MetadataInfo(cfdp::FileSize& fileSize, cfdp::StringLv& sourceFileName,
-               cfdp::StringLv& destFileName);
-  MetadataInfo(bool closureRequested, cfdp::ChecksumType checksumType, cfdp::FileSize& fileSize,
+  MetadataInfo(cfdp::Fss& fileSize, cfdp::StringLv& sourceFileName, cfdp::StringLv& destFileName);
+  MetadataInfo(bool closureRequested, cfdp::ChecksumType checksumType, cfdp::Fss& fileSize,
                cfdp::StringLv& sourceFileName, cfdp::StringLv& destFileName);
 
   size_t getSerializedSize(bool fssLarge = false);
@@ -30,7 +29,7 @@ class MetadataInfo {
 
   cfdp::StringLv& getDestFileName();
   cfdp::StringLv& getSourceFileName();
-  cfdp::FileSize& getFileSize();
+  cfdp::Fss& getFileSize();
 
   [[nodiscard]] bool hasOptions() const;
   [[nodiscard]] bool canHoldOptions() const;
@@ -43,7 +42,7 @@ class MetadataInfo {
  private:
   bool closureRequested = false;
   cfdp::ChecksumType checksumType = cfdp::ChecksumType::NULL_CHECKSUM;
-  cfdp::FileSize& fileSize;
+  cfdp::Fss& fileSize;
   cfdp::StringLv& sourceFileName;
   cfdp::StringLv& destFileName;
 
diff --git a/src/fsfw/cfdp/pdu/NakInfo.cpp b/src/fsfw/cfdp/pdu/NakInfo.cpp
index 14d06cb0..8ae317f4 100644
--- a/src/fsfw/cfdp/pdu/NakInfo.cpp
+++ b/src/fsfw/cfdp/pdu/NakInfo.cpp
@@ -1,6 +1,6 @@
 #include "NakInfo.h"
 
-NakInfo::NakInfo(cfdp::FileSize startOfScope, cfdp::FileSize endOfScope)
+NakInfo::NakInfo(cfdp::Fss startOfScope, cfdp::Fss endOfScope)
     : startOfScope(startOfScope), endOfScope(endOfScope) {}
 
 size_t NakInfo::getSerializedSize(bool fssLarge) {
@@ -57,9 +57,9 @@ void NakInfo::setSegmentRequests(SegmentRequest* segmentRequests, size_t* segmen
   }
 }
 
-cfdp::FileSize& NakInfo::getStartOfScope() { return startOfScope; }
+cfdp::Fss& NakInfo::getStartOfScope() { return startOfScope; }
 
-cfdp::FileSize& NakInfo::getEndOfScope() { return endOfScope; }
+cfdp::Fss& NakInfo::getEndOfScope() { return endOfScope; }
 
 size_t NakInfo::getSegmentRequestsLen() const { return segmentRequestsLen; }
 
diff --git a/src/fsfw/cfdp/pdu/NakInfo.h b/src/fsfw/cfdp/pdu/NakInfo.h
index 02d6b6f4..f8f6b147 100644
--- a/src/fsfw/cfdp/pdu/NakInfo.h
+++ b/src/fsfw/cfdp/pdu/NakInfo.h
@@ -3,21 +3,21 @@
 
 #include <utility>
 
-#include "fsfw/cfdp/FileSize.h"
+#include "fsfw/cfdp/Fss.h"
 
 class NakInfo {
  public:
-  using SegmentRequest = std::pair<cfdp::FileSize, cfdp::FileSize>;
+  using SegmentRequest = std::pair<cfdp::Fss, cfdp::Fss>;
 
-  NakInfo(cfdp::FileSize startOfScope, cfdp::FileSize endOfScope);
+  NakInfo(cfdp::Fss startOfScope, cfdp::Fss endOfScope);
 
   void setSegmentRequests(SegmentRequest* segmentRequests, size_t* segmentRequestLen,
                           size_t* maxSegmentRequestLen);
 
   size_t getSerializedSize(bool fssLarge = false);
 
-  cfdp::FileSize& getStartOfScope();
-  cfdp::FileSize& getEndOfScope();
+  cfdp::Fss& getStartOfScope();
+  cfdp::Fss& getEndOfScope();
 
   bool hasSegmentRequests() const;
   bool canHoldSegmentRequests() const;
@@ -31,8 +31,8 @@ class NakInfo {
   void setSegmentRequestLen(size_t readLen);
 
  private:
-  cfdp::FileSize startOfScope;
-  cfdp::FileSize endOfScope;
+  cfdp::Fss startOfScope;
+  cfdp::Fss endOfScope;
   SegmentRequest* segmentRequests = nullptr;
   size_t segmentRequestsLen = 0;
   size_t maxSegmentRequestsLen = 0;
diff --git a/src/fsfw/cfdp/pdu/NakPduCreator.h b/src/fsfw/cfdp/pdu/NakPduCreator.h
index bfcff78d..601078fc 100644
--- a/src/fsfw/cfdp/pdu/NakPduCreator.h
+++ b/src/fsfw/cfdp/pdu/NakPduCreator.h
@@ -4,7 +4,7 @@
 #include <vector>
 
 #include "NakInfo.h"
-#include "fsfw/cfdp/FileSize.h"
+#include "fsfw/cfdp/Fss.h"
 #include "fsfw/cfdp/definitions.h"
 #include "fsfw/cfdp/pdu/FileDirectiveCreator.h"
 
diff --git a/unittests/cfdp/handler/testDestHandler.cpp b/unittests/cfdp/handler/testDestHandler.cpp
index d0aea3d5..792d919c 100644
--- a/unittests/cfdp/handler/testDestHandler.cpp
+++ b/unittests/cfdp/handler/testDestHandler.cpp
@@ -50,7 +50,7 @@ TEST_CASE("CFDP Dest Handler", "[cfdp]") {
   auto destHandler = DestHandler(dp, fp);
   CHECK(destHandler.initialize() == OK);
 
-  auto metadataPreparation = [&](FileSize cfdpFileSize, ChecksumType checksumType) {
+  auto metadataPreparation = [&](Fss cfdpFileSize, ChecksumType checksumType) {
     std::string srcNameString = "hello.txt";
     std::string destNameString = "hello-cpy.txt";
     StringLv srcName(srcNameString);
@@ -91,7 +91,7 @@ TEST_CASE("CFDP Dest Handler", "[cfdp]") {
     REQUIRE(res.step == DestHandler::TransactionStep::RECEIVING_FILE_DATA_PDUS);
   };
 
-  auto eofPreparation = [&](FileSize cfdpFileSize, uint32_t crc) {
+  auto eofPreparation = [&](Fss cfdpFileSize, uint32_t crc) {
     EofInfo eofInfo(cfdp::ConditionCode::NO_ERROR, crc, std::move(cfdpFileSize));
     EofPduCreator eofCreator(conf, eofInfo);
     REQUIRE(tcStore.getFreeElement(&storeId, eofCreator.getSerializedSize(), &buf) == OK);
@@ -145,7 +145,7 @@ TEST_CASE("CFDP Dest Handler", "[cfdp]") {
   SECTION("Empty File Transfer") {
     const DestHandler::FsmResult& res = destHandler.performStateMachine();
     CHECK(res.result == OK);
-    FileSize cfdpFileSize(0);
+    Fss cfdpFileSize(0);
     metadataPreparation(cfdpFileSize, ChecksumType::NULL_CHECKSUM);
     destHandler.performStateMachine();
     metadataCheck(res, "hello.txt", "hello-cpy.txt", 0);
@@ -165,14 +165,14 @@ TEST_CASE("CFDP Dest Handler", "[cfdp]") {
     etl::crc32 crcCalc;
     crcCalc.add(fileData.begin(), fileData.end());
     uint32_t crc32 = crcCalc.value();
-    FileSize cfdpFileSize(fileData.size());
+    Fss cfdpFileSize(fileData.size());
     metadataPreparation(cfdpFileSize, ChecksumType::CRC_32);
     destHandler.performStateMachine();
     metadataCheck(res, "hello.txt", "hello-cpy.txt", fileData.size());
     destHandler.performStateMachine();
     REQUIRE(res.callStatus == CallStatus::CALL_AFTER_DELAY);
     auto transactionId = destHandler.getTransactionId();
-    FileSize offset(0);
+    Fss offset(0);
     FileDataInfo fdPduInfo(offset, reinterpret_cast<const uint8_t*>(fileData.data()),
                            fileData.size());
     FileDataCreator fdPduCreator(conf, fdPduInfo);
@@ -201,7 +201,7 @@ TEST_CASE("CFDP Dest Handler", "[cfdp]") {
     etl::crc32 crcCalc;
     crcCalc.add(largerFileData.begin(), largerFileData.end());
     uint32_t crc32 = crcCalc.value();
-    FileSize cfdpFileSize(largerFileData.size());
+    Fss cfdpFileSize(largerFileData.size());
     metadataPreparation(cfdpFileSize, ChecksumType::CRC_32);
     destHandler.performStateMachine();
     metadataCheck(res, "hello.txt", "hello-cpy.txt", largerFileData.size());
@@ -211,7 +211,7 @@ TEST_CASE("CFDP Dest Handler", "[cfdp]") {
 
     std::vector<store_address_t> idsToCheck;
     {
-      FileSize offset(0);
+      Fss offset(0);
       FileDataInfo fdPduInfo(offset, reinterpret_cast<const uint8_t*>(largerFileData.data()),
                              largerFileData.size() / 2);
       FileDataCreator fdPduCreator(conf, fdPduInfo);
@@ -223,7 +223,7 @@ TEST_CASE("CFDP Dest Handler", "[cfdp]") {
     }
 
     {
-      FileSize offset(512);
+      Fss offset(512);
       FileDataInfo fdPduInfo(offset, reinterpret_cast<const uint8_t*>(largerFileData.data() + 512),
                              largerFileData.size() / 2);
       FileDataCreator fdPduCreator(conf, fdPduInfo);
diff --git a/unittests/cfdp/handler/testDistributor.cpp b/unittests/cfdp/handler/testDistributor.cpp
index 8b6c46af..04c035a7 100644
--- a/unittests/cfdp/handler/testDistributor.cpp
+++ b/unittests/cfdp/handler/testDistributor.cpp
@@ -21,7 +21,7 @@ TEST_CASE("CFDP Distributor", "[cfdp][distributor]") {
   auto tcAcceptor = AcceptsTcMock("CFDP Receiver", 0, receiverQueueId);
 
   // Set up Metadata PDU for generate test data.
-  cfdp::FileSize fileSize(12);
+  cfdp::Fss fileSize(12);
   const cfdp::EntityId& sourceId(groundEntityId);
   const cfdp::EntityId& destId(obswEntityId);
   cfdp::TransactionSeqNum seqNum(UnsignedByteField<uint16_t>(12));
diff --git a/unittests/cfdp/pdu/testEofPdu.cpp b/unittests/cfdp/pdu/testEofPdu.cpp
index 83e61780..0eb0342b 100644
--- a/unittests/cfdp/pdu/testEofPdu.cpp
+++ b/unittests/cfdp/pdu/testEofPdu.cpp
@@ -14,7 +14,7 @@ TEST_CASE("EOF PDU", "[cfdp][pdu]") {
   size_t sz = 0;
   EntityId destId(WidthInBytes::TWO_BYTES, 2);
   EntityIdTlv faultLoc(destId);
-  FileSize fileSize(12);
+  Fss fileSize(12);
   // We can already set the fault location, it will be ignored
   EofInfo eofInfo(cfdp::ConditionCode::NO_ERROR, 5, fileSize, &faultLoc);
   TransactionSeqNum seqNum(WidthInBytes::TWO_BYTES, 15);
diff --git a/unittests/cfdp/pdu/testFileData.cpp b/unittests/cfdp/pdu/testFileData.cpp
index 39139378..6eed1dd3 100644
--- a/unittests/cfdp/pdu/testFileData.cpp
+++ b/unittests/cfdp/pdu/testFileData.cpp
@@ -22,7 +22,7 @@ TEST_CASE("File Data PDU", "[cfdp][pdu]") {
   for (uint8_t idx = 0; idx < 10; idx++) {
     fileBuffer[idx] = idx;
   }
-  FileSize offset(50);
+  Fss offset(50);
   FileDataInfo info(offset, fileBuffer.data(), 10);
 
   SECTION("Serialization") {
@@ -107,7 +107,7 @@ TEST_CASE("File Data PDU", "[cfdp][pdu]") {
         serializer.serialize(&buffer, &sz, fileDataBuffer.size(), SerializeIF::Endianness::NETWORK);
     REQUIRE(result == returnvalue::OK);
 
-    FileSize emptyOffset;
+    Fss emptyOffset;
     FileDataInfo emptyInfo(emptyOffset);
     FileDataReader deserializer(fileDataBuffer.data(), fileDataBuffer.size(), emptyInfo);
     result = deserializer.parseData();
diff --git a/unittests/cfdp/pdu/testKeepAlivePdu.cpp b/unittests/cfdp/pdu/testKeepAlivePdu.cpp
index d07bccae..f8eeda42 100644
--- a/unittests/cfdp/pdu/testKeepAlivePdu.cpp
+++ b/unittests/cfdp/pdu/testKeepAlivePdu.cpp
@@ -16,7 +16,7 @@ TEST_CASE("Keep Alive PDU", "[cfdp][pdu]") {
   EntityId sourceId(WidthInBytes::TWO_BYTES, 1);
   PduConfig pduConf(sourceId, destId, TransmissionMode::ACKNOWLEDGED, seqNum);
 
-  FileSize progress(0x50);
+  Fss progress(0x50);
 
   SECTION("Serialize") {
     KeepAlivePduCreator serializer(pduConf, progress);
diff --git a/unittests/cfdp/pdu/testMetadataPdu.cpp b/unittests/cfdp/pdu/testMetadataPdu.cpp
index a9f8bf86..747a2dc3 100644
--- a/unittests/cfdp/pdu/testMetadataPdu.cpp
+++ b/unittests/cfdp/pdu/testMetadataPdu.cpp
@@ -22,7 +22,7 @@ TEST_CASE("Metadata PDU", "[cfdp][pdu]") {
   std::string firstFileName = "hello.txt";
   cfdp::StringLv sourceFileName(firstFileName);
   cfdp::StringLv destFileName;
-  FileSize fileSize(35);
+  Fss fileSize(35);
   MetadataInfo info(false, ChecksumType::MODULAR, fileSize, sourceFileName, destFileName);
 
   FilestoreResponseTlv response(FilestoreActionCode::CREATE_DIRECTORY, FSR_CREATE_NOT_ALLOWED,
diff --git a/unittests/cfdp/pdu/testNakPdu.cpp b/unittests/cfdp/pdu/testNakPdu.cpp
index 7974dab1..c3650c63 100644
--- a/unittests/cfdp/pdu/testNakPdu.cpp
+++ b/unittests/cfdp/pdu/testNakPdu.cpp
@@ -17,8 +17,8 @@ TEST_CASE("NAK PDU", "[cfdp][pdu]") {
   EntityId sourceId(WidthInBytes::TWO_BYTES, 1);
   PduConfig pduConf(sourceId, destId, TransmissionMode::ACKNOWLEDGED, seqNum);
 
-  FileSize startOfScope(50);
-  FileSize endOfScope(1050);
+  Fss startOfScope(50);
+  Fss endOfScope(1050);
   NakInfo info(startOfScope, endOfScope);
   SECTION("Serializer") {
     NakPduCreator serializer(pduConf, info);
@@ -40,8 +40,8 @@ TEST_CASE("NAK PDU", "[cfdp][pdu]") {
     REQUIRE(result == returnvalue::OK);
     REQUIRE(scope == 1050);
 
-    NakInfo::SegmentRequest segReq0(cfdp::FileSize(2020), cfdp::FileSize(2520));
-    NakInfo::SegmentRequest segReq1(cfdp::FileSize(2932), cfdp::FileSize(3021));
+    NakInfo::SegmentRequest segReq0(cfdp::Fss(2020), cfdp::Fss(2520));
+    NakInfo::SegmentRequest segReq1(cfdp::Fss(2932), cfdp::Fss(3021));
     // Now add 2 segment requests to NAK info and serialize them as well
     std::array<NakInfo::SegmentRequest, 2> segReqs = {segReq0, segReq1};
     size_t segReqsLen = segReqs.size();
@@ -100,8 +100,8 @@ TEST_CASE("NAK PDU", "[cfdp][pdu]") {
     REQUIRE(info.getStartOfScope().getSize() == 50);
     REQUIRE(info.getEndOfScope().getSize() == 1050);
 
-    NakInfo::SegmentRequest segReq0(cfdp::FileSize(2020), cfdp::FileSize(2520));
-    NakInfo::SegmentRequest segReq1(cfdp::FileSize(2932), cfdp::FileSize(3021));
+    NakInfo::SegmentRequest segReq0(cfdp::Fss(2020), cfdp::Fss(2520));
+    NakInfo::SegmentRequest segReq1(cfdp::Fss(2932), cfdp::Fss(3021));
     // Now add 2 segment requests to NAK info and serialize them as well
     std::array<NakInfo::SegmentRequest, 2> segReqs = {segReq0, segReq1};
     size_t segReqsLen = segReqs.size();
diff --git a/unittests/cfdp/testCfdp.cpp b/unittests/cfdp/testCfdp.cpp
index 467b5b2d..60b14b77 100644
--- a/unittests/cfdp/testCfdp.cpp
+++ b/unittests/cfdp/testCfdp.cpp
@@ -2,7 +2,7 @@
 #include <catch2/catch_test_macros.hpp>
 #include <cstring>
 
-#include "fsfw/cfdp/FileSize.h"
+#include "fsfw/cfdp/Fss.h"
 #include "fsfw/cfdp/pdu/FileDirectiveCreator.h"
 #include "fsfw/cfdp/pdu/FileDirectiveReader.h"
 #include "fsfw/globalfunctions/arrayprinter.h"
@@ -79,7 +79,7 @@ TEST_CASE("CFDP Base", "[cfdp]") {
     std::array<uint8_t, 8> fssBuf = {};
     uint8_t* buffer = fssBuf.data();
     size_t size = 0;
-    cfdp::FileSize fss;
+    cfdp::Fss fss;
     REQUIRE(fss.getSize() == 0);
     fss.setFileSize(0x20, false);
     result = fss.serialize(&buffer, &size, fssBuf.size(), SerializeIF::Endianness::MACHINE);