This article explains the difference in session counts between show sub and show session progress commands on an HSGW.
Call ID is the entity used on ASR5K platform to represent a call session. On Packet Data Network Gateway (PGW), there is a unique Call ID for each Application Point Name (APN) connection for a particular subscriber International Mobile Session Identifier (IMSI). Conversely, on an eHRPD Serving Gateway (HSGW), all the APNs share the same Call ID for an IMSI. Since show sub commands report on a sub-session basis, the counts from this command properly reflect the total number of APN connections. Conversely, show session progress reports on a Call ID basis, and so counts will be lower than compared with PGW and will not reflect the total number of APNs.
On a PGW, APN connections are counted separately from one another for the same IMSI for show subscriber commands and "show session progress". Here is an example of a single subscriber connected over three different APNs, and therefore assigned three separate Call IDs. Note the values for the Call IDs can be close in proximity for a given IMSI.
In the following output, Long Term Evolution (LTE) (gtp) and Evolved High Rate Packet Data (eHRPD) (pmip) counts are seen on a PGW. The values can be corroborated between show sub sum and show session progress:
[local]PGW> show subscriber summary
Total Subscribers: 3822449
Active: 3822449 Dormant: 0
pdsn-simple-ipv4: 0 pdsn-simple-ipv6: 0
pdsn-mobile-ip: 0 ha-mobile-ipv6: 0
hsgw-ipv6: 0 hsgw-ipv4: 0
hsgw-ipv4-ipv6: 0 pgw-pmip-ipv6: 258454
pgw-pmip-ipv4: 209 pgw-pmip-ipv4-ipv6: 220120
pgw-gtp-ipv6: 1793806 pgw-gtp-ipv4: 6701
pgw-gtp-ipv4-ipv6: 1543679 sgw-gtp-ipv6: 0
[local]PGW> show session progress
3821347 In-progress calls
6909 In-progress calls @ PDN-TYPE-IPv4 CONNECTED state
2051456 In-progress calls @ PDN-TYPE-IPv6 CONNECTED state
1762878 In-progress calls @ PDN-TYPE-IPv4+IPv6 CONNECTED state
1793806 + 258454 = 2052260
1543679 + 220120 = 1763799
As mentioned, on an HSGW, the same Call ID is shared for all APNs belonging to a given IMSI. The reason for this is that at the time the session is created, when the initial RRQ comes in and initiates the authentication to AAA (over STa), the HSGW only knows about the IMSI. The APN info comes later when PPP VSNCP phase starts. Hence all the APNs (i.e PDN) which belong to the same IMSI are treated as one session on the HSGW.
In this output there are two subscribers each connected via two APNs, and while the APN names are NOT tracked by the HSGW, their IP types (IPv4, IPv6, or IPv4+IPv6) are known and show sub commands properly reflect that:
Comparing output from "show sub summary" and "show session progress", the latter output reports much lower numbers for SIMPLE-IPv6 than for the analogous hsgw-ipv6 from show sub summary ...
Note that the count for hsgw-ipv4-ipv6 is essentially the same as SIMPLE-IPv4+IPv6, while hsgw-ipv6 is much larger than SIMPLE-IPv6. As it turns out, if a particular IMSI is connected as an IPv4/IPv6-based APN, then it gets counted under SIMPLE-IPv4+IPv6, while if it is ALSO connected as an IPv6-based APN (i.e. the IMS session), then it does NOT also get counted as SIMPLE-IPv6. It only gets counted as SIMPLE-IPv6 if there is no corresponding IPv4+IPv6 (or IPv4) connection. In other words, show session progress will only report one call per IMSI, regardless of the number of APN connections for that IMSI. This ultimately stems from the fact that there is one Call ID per IMSI on HSGW.
[HSGWin]HSGW> show sub summary
Total Subscribers: 460307
Active: 39756 Dormant: 420551
hsgw-ipv6: 247972 hsgw-ipv4: 1632
hsgw-ipv4-ipv6: 209968 pgw-pmip-ipv6: 0
[HSGWin]HSGW> show session progress
255045 In-progress calls
20713 In-progress active calls
234332 In-progress dormant calls
811 In-progress calls @ LCP-NEG state
84 In-progress calls @ LCP-UP state
276 In-progress calls @ AUTHENTICATING state
0 In-progress calls @ BCMCS SERVICE AUTHENTICATING state
270 In-progress calls @ AUTHENTICATED state
72 In-progress calls @ SIMPLE-IPv4 CONNECTED state
43944 In-progress calls @ SIMPLE-IPv6 CONNECTED state
209555 In-progress calls @ SIMPLE-IPv4+IPv6 CONNECTED state
The above is made clearer when looking at the output from a combo HSGW-PGW LAB node with one only connected IMSI with three APNs. show sub summary reports ALL six sub-sessions, three for HSGW and three for PGW. The underlying difference is that the HSGW sessions all share the same Call ID, while for the PGW the Call IDs are unique.
Meanwhile for "show session progress", four calls are reported, three for the APNs on PGW, and one for the IPv4+IPv6 APN on the HSGW which effectively represents ALL three HSGW APNs, giving a total of four sessions instead of the actual six reported by show sub commands.