This is on the CSC downloads site available after signing in to the Spirent CSC at http://support.spirent.com/.
There are many more details you can find on the Internet pertaining to MD5 and SHA-1 checksums, but in short, MD5/SHA1 checksums are generated through hashing algorithms that create a unique checksum for a file. If even one bit changes in a file, even for very large files, the checksum changes as well. Of the two, MD5 is more common, but SHA-1 is growing in popularity since it has a higher mathematical chance of generating a unique checksum.
Before we put our files on the server for you to download, we run the files through the standard MD5/SHA1 hashing algorithms to generate the checksum strings, which is then offered to you when you download.
If you want to verify file integrity and don't already have something to generate the checksum after a download, do an Internet search for "MD5 checksum utility" or "SHA-1 checksum utility", where you'll find dozens of possibilities, several of them offering both MD5 and SHA-1 checksums in the same tool.
Of note: the free Spirent Download Manager can perform a checksum integrity check for you-- in the interface, click on the file you want to check, then press Shift-I, then paste the checksum: