[SR-Users] [Mod: CDP] TCP Zero Window Error

Dear Users I have been facing a diameter peer disconnection issue between I-CSCF and HSS. after taking traces on both sides, I saw a lot of TCP Zero Window packets from HSS towards I-CSCF and after that HSS disconnects with the following errors in the log. Nov 26 20:30:25 PROD-HSS-STANDBY [HSS][16401]: ERROR: cdp [peerstatemachine.c:157]: sm_process(): sm_process(): In state Closed invalid event Timeout Nov 26 20:31:25 PROD-HSS-STANDBY [HSS][16401]: ERROR: cdp [peerstatemachine.c:157]: sm_process(): sm_process(): In state Closed invalid event Timeout Nov 26 20:32:25 PROD-HSS-STANDBY [HSS][16401]: ERROR: cdp [peerstatemachine.c:157]: sm_process(): sm_process(): In state Closed invalid event Timeout Nov 26 20:33:04 PROD-HSS-STANDBY systemd[1]: Stopping LSB: Start the Kamailio SIP proxy server... Nov 26 20:33:04 PROD-HSS-STANDBY kamailio_hss[18098]: Stopping Kamailio SIP Server: kamailio_hss:. Nov 26 20:33:04 PROD-HSS-STANDBY systemd[1]: kamailio_hss.service: Succeeded. Nov 26 20:33:04 PROD-HSS-STANDBY systemd[1]: Stopped LSB: Start the Kamailio SIP proxy server. Nov 26 20:33:04 PROD-HSS-STANDBY [HSS][16274]: CRITICAL: cdp [diameter_peer.c:423]: diameter_peer_destroy(): destroy_diameter_peer(): Bye Bye from C Diameter Peer test Nov 26 20:33:07 PROD-HSS-STANDBY systemd[1]: Starting LSB: Start the Kamailio SIP proxy server... Nov 26 20:33:07 PROD-HSS-STANDBY kamailio_hss[18138]: Starting Kamailio SIP Server: kamailio_hss:loading modules under config path: /usr/local/lib64/kamailio/modules/:/usr/lib64/kamailio/modules_k/:/usr/lib64/kamailio/modules/:/usr/local/lib/kamailio/modules/ Nov 26 20:33:07 PROD-HSS-STANDBY kamailio_hss[18138]: Listening on Nov 26 20:33:07 PROD-HSS-STANDBY kamailio_hss[18138]: udp: 10.161.224.81 [10.161.224.81]:8080 Nov 26 20:33:07 PROD-HSS-STANDBY kamailio_hss[18138]: tcp: 127.0.0.1 [127.0.0.1]:5090 Nov 26 20:33:07 PROD-HSS-STANDBY kamailio_hss[18138]: tcp: 10.161.224.81 [10.161.224.81]:8080 Nov 26 20:33:07 PROD-HSS-STANDBY kamailio_hss[18138]: Aliases: Nov 26 20:33:07 PROD-HSS-STANDBY [HSS][18155]: WARNING: sl [../../modules/tm/tm_load.h:149]: load_tm_api(): Cannot import load_tm function from tm module Nov 26 20:33:07 PROD-HSS-STANDBY [HSS][18155]: WARNING: sl [../../modules/tm/tm_load.h:149]: load_tm_api(): Cannot import load_tm function from tm module Nov 26 20:33:07 PROD-HSS-STANDBY [HSS][18281]: WARNING: cdp [tcp_accept.c:120]: create_socket(): create_socket(): Trying to open/bind/listen on 10.161.224.81 port 3868 Nov 26 20:33:07 PROD-HSS-STANDBY [HSS][18281]: WARNING: cdp [tcp_accept.c:145]: create_socket(): create_socket(): Successful socket open/bind/listen on 10.161.224.81 port 3868 Nov 26 20:33:07 PROD-HSS-STANDBY kamailio_hss[18138]: . Nov 26 20:33:07 PROD-HSS-STANDBY systemd[1]: Started LSB: Start the Kamailio SIP proxy server. Nov 26 20:38:44 PROD-HSS-STANDBY [HSS][18282]: WARNING: cdp [peermanager.c:310]: peer_timer(): Inactivity on peer [icscfcdp2.ims.mnc006.mcc410.3gppnetwork.org] and no DWA, Closing peer... Nov 26 20:39:01 PROD-HSS-STANDBY systemd[1]: Starting Clean php session files... Nov 26 20:39:01 PROD-HSS-STANDBY systemd[1]: phpsessionclean.service: Succeeded. Nov 26 20:39:01 PROD-HSS-STANDBY systemd[1]: Started Clean php session files. Nov 26 20:39:20 PROD-HSS-STANDBY [HSS][18282]: ERROR: cdp [peerstatemachine.c:157]: sm_process(): sm_process(): In state Closed invalid event Timeout I am using the following Kamailio version Distributor ID: Debian Description: Debian GNU/Linux 10 (buster) Release: 10 Codename: buster Version: kamailio 5.2.8 (x86_64/linux) 5a7f5b Default config: /usr/local/etc/kamailio/kamailio.cfg Default paths to modules: /usr/local/lib64/kamailio/modules Compile flags: STATS: Off, USE_TCP, USE_TLS, USE_SCTP, TLS_HOOKS, USE_RAW_SOCKS, DISABLE_NAGLE, USE_MCAST, DNS_IP_HACK, SHM_MEM, SHM_MMAP, PKG_MALLOC, Q_MALLOC, F_MALLOC, TLSF_MALLOC, DBG_SR_MEMORY, USE_FUTEX, FAST_LOCK-ADAPTIVE_WAIT, USE_DNS_CACHE, USE_DNS_FAILOVER, USE_NAPTR, USE_DST_BLACKLIST, HAVE_RESOLV_RES MAX_RECV_BUFFER_SIZE=262144 MAX_URI_SIZE=1024 BUF_SIZE=65535 DEFAULT PKG_SIZE=8MB DEFAULT SHM_SIZE=64MB ADAPTIVE_WAIT_LOOPS=1024 TCP poll methods: poll, epoll_lt, epoll_et, sigio_rt, select Source code revision ID: 5a7f5b Compiled with: gcc 8.3.0 Compiled on: 04:34:39 Nov 19 2020 How I can resolve TCP Zero Window Error? I have already tried increasing CDP worker threads, TCP read and write buffers etc. Regards Hamid R. Hashmi